1. Field of the Invention
The present invention relates to a conditioning method and apparatus of a polishing pad, and more particularly to a method and apparatus for conditioning a surface of a polishing pad used for polishing a substrate such as a semiconductor wafer.
2. Description of the Related Art
In recent years, high integration and high density in semiconductor device demands smaller and smaller wiring patterns or interconnections and also more and more interconnection layers. Multilayer interconnections in smaller circuits result in greater steps which reflect surface irregularities on lower interconnection layers. An increase in the number of interconnection layers makes film coating performance (step coverage) poor over stepped configurations of thin films. Therefore, better multilayer interconnections need to have the improved step coverage and proper surface planarization. Further, since the depth of focus of a photolithographic optical system is smaller with miniaturization of a photolithographic process, a surface of the semiconductor device needs to be planarized such that irregular steps on the surface of the semiconductor device will fall within the depth of focus.
Thus, in a manufacturing process of a semiconductor device, it increasingly becomes important to planarize a surface of the semiconductor device. One of the most important planarizing technologies is chemical mechanical polishing (CMP). Thus, there has been employed a chemical mechanical polishing apparatus for planarizing a surface of a semiconductor wafer. In the chemical mechanical polishing apparatus, while a polishing liquid containing abrasive particles such as ceria (CeO2) therein is supplied onto a polishing pad, a substrate such as a semiconductor wafer is brought into sliding contact with the polishing pad, so that the substrate is polished.
A polishing apparatus for performing the above CMP process includes a polishing table having a polishing pad, and a substrate holding device, which is referred to as a top ring or a polishing head, for holding a substrate such as a semiconductor wafer. By using such a polishing apparatus, the substrate is held and pressed against the polishing pad under a predetermined pressure by the substrate holding device, thereby polishing an insulating film or a metal film on the substrate.
After one or more substrates have been polished, abrasive particles in a polishing liquid or ground-off particles of the substrate are attached to the surface of the polishing pad, resulting in a change in properties of the polishing pad and deterioration in polishing performance. Therefore, as the substrates are repeatedly polished by the same polishing pad, a polishing rate is lowered and nonuniform polishing action is caused. Thus, conditioning (also referred to as dressing) of the polishing pad is performed to regenerate the surface of the polishing pad which has deteriorated.
A conditioning apparatus (dressing apparatus) for performing conditioning (dressing) of the polishing pad generally has a swingable arm and a dresser fixed to a forward end of the arm as disclosed in Japanese laid-open patent publication No. 2002-200552. In a conditioning process performed by the conditioning apparatus, while the dresser is oscillated radially of the polishing pad by the arm and is rotated about its axis, the dresser is pressed against the polishing pad on the rotating polishing table to remove the abrasive particles and the ground-off particles attached to the polishing pad and to flatten and dress the polishing pad. In general, the dresser having a surface (dressing surface), being brought into contact with the pad surface, on which diamond particles are electrodeposited is used.
In the conventional conditioning apparatus (dressing apparatus), in the case where the dresser is oscillated radially of the polishing pad, in order to maximize the life of the polishing pad, the oscillating speed of the dresser is adjusted so that the entire pad surface is uniformly dressed and the polishing pad is worn down flat.
The present inventors have repeatedly conducted experiments of polishing substrates by using the polishing pads which have been conditioned (dressed) by the dresser whose oscillating speed has been adjusted to enable each of the polishing pads to be worn down flat. As a result, the present inventors have learned that a supply amount of a polishing liquid (slurry) to a central part of the substrate becomes scarce due to the relationship between a polishing pressure, respective rotating speeds of the polishing table and the top ring, and the shape of grooves or holes in the surface of the polishing pad, and thus uniform polishing rate cannot be obtained over the entire surface of the substrate.
In particular, in the ceria CMP process in which the polishing pad, called a perforated pad, having a number of small holes in the surface of the polishing pad is used and the substrate is polished while a polishing liquid containing ceria (CeO2) as abrasive particles is supplied to the polishing pad, in the case of high-pressure polishing for polishing the substrate by pressing the substrate against the polishing pad at a high-pressure of 400 hPa or higher, it is difficult for the polishing liquid (slurry) to enter the central part of the surface, being polished, of the substrate. Therefore, an amount of the polishing liquid (slurry) becomes scarce to lower the polishing rate at the central part of the surface, being polished, of the substrate, resulting in nonuniform polishing rate in the entire substrate.
Further, as in the case where an insulating film or a metal film having a relatively large thickness on the substrate is removed, when prolonged polishing is required, the polishing performance of the ceria abrasive particles is lowered due to temperature rise of the surface of the polishing pad, and supply capacity of the polishing liquid (slurry) is lowered with time due to a change in surface state of the polishing pad.